What length antenna for 915 mhz?

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tburt11
Posts: 2
Joined: Mon Jun 03, 2013 2:59 pm

What length antenna for 915 mhz?

Post by tburt11 » Mon Jun 03, 2013 3:24 pm

My apologies if this is described elsewhere. I have googled and I have read, and I cannot find the answer.

I purchased a few jeenodes v5 and a jeelink v2 a few years ago, and then never got around to using them. I do not remember what frequency I ordered, it was too long ago.

Now I have them up and running, but I only get about 6 feet of range. They are both set to 915 Mhz as programmed with the default demo.

I googled "Jeenode red dot" and I got:

// red dots on radios are 915Mhz, green dots are 434 Mhz

The JeeNode modules have an antenna that is about 88 mm in length. The antenna on the JeeLink measures about 112 mm.

I found a reference that states:

82mm for 868Mhz and 78mm for 915Mhz

I am confused. If I have a red dot on the radio smd, what length should my antenna be? Why does my pre-assembled JeeLink have a 112 mm antenna?

Should I trim both of these down to 78 mm?

Thanks in advance!

tburt11
Posts: 2
Joined: Mon Jun 03, 2013 2:59 pm

Re: What length antenna for 915 mhz?

Post by tburt11 » Mon Jun 03, 2013 3:46 pm

Ok, I answered my own question. At least the easy part.

I pried open the JeeLink and soldered on my own 78 mm wire, and replaced the antenna on the JeeNode with 78 mm. Now I am getting a nice 50 feet through two outer walls dependable signal. Good enough for my purposes.

My unanswered question would be....

Why is the JeeLink shipped with an antenna that is not tuned for the frequency of the radio?

I hope this post helps somebody else.

paul
Site Admin
Posts: 730
Joined: Mon May 12, 2008 4:19 pm

Re: What length antenna for 915 mhz?

Post by paul » Thu Jun 20, 2013 1:30 pm

tburt11,

Sorry about the really slow reply - I just saw this slipped through the cracks.
Why is the JeeLink shipped with an antenna that is not tuned for the frequency of the radio?
It should be in the range of 80 mm. We have found it doesn't matter that much as long as it's close.
Apparently someone in production wasn't using our cutting jig very carefully. As you originally asked, it's easy to cut down the wire to the precise length.

I'll make sure production people know about that tolerance.

Paul

JeffreyKip
Posts: 3
Joined: Tue Apr 11, 2017 6:13 am

What length antenna for 915 mhz

Post by JeffreyKip » Tue Apr 18, 2017 9:06 am

Hi, I have a second-hand JETI REX 5 plus receiver which looks like it has had the antenna shortened. Would anyone know what the original length should be? Many thanks

Remilqdmv
Posts: 7
Joined: Wed Sep 20, 2017 7:26 pm

What length antenna for 915 mhz

Post by Remilqdmv » Fri Sep 29, 2017 12:49 pm

Thanks Tim - I'll check. This is just a stopgap measure for me as things are coming at us quickly.

I know we have to vacate. 600MHz by end of 2018...


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